A few winters ago, it rained pretty much constantly for three months. By month two of the unrelentingly wet weather, my thoughts had also taken a predictably dour turn. Inside my head, I heard the same unpleasant soundtrack over and over: What if the economy doesn’t turn around? Why is my husband working such long hours? When did my belly get so flabby? My brain was a scratched CD, and the longer the negative track went on, the worse I felt. I’d like to say that normally I’m an optimistic and sunny person. But the truth is, my mind naturally tilts in the direction of worry. The endless rain simply pushed me more firmly toward the bleak side.

Given my morose mood, it’s surprising that I even noticed the new addition to the fenced-in field at the entrance of our otherwise suburban San Francisco Bay–area subdivision. But one day, as I was driving past the field, I saw her: a black potbellied pig. I later learned that the pig’s name was Chloe, and on that soggy day, she was frolicking in the rain, black snout snuffling deliriously in the soaked grass. I’m not one to throw around phrases such as “my heart leapt,” but that’s exactly what mine did, and my mind did, too. Suddenly, my brain cells were singing the “Hallelujah” chorus. I was so captivated, I pulled over to watch, basking in my little pocket of unexpected joy. Over the next few weeks, I tried to catch glimpses of Chloe’s comical body any time I could, and when I didn’t see her, I’d replay a mental image of her cavorting in the rain. The thought made me smile, jolting me out of my gloom. It’s not that I felt chipper exactly, but I was a tad more hopeful. I couldn’t help but wonder, Had a pig suddenly turned my sodden mood sunny?

Neuroscientists would say that the ebullient little animal was indeed a happiness catalyst, if only because she nudged me out of my negative rut. And scientists increasingly believe that what we think—both the good stuff and the bad—sculpts our brain circuitry, which, in turn, can reshape our overall outlook.

Not that it’s quite as easy as “think happy thoughts and you’ll end up happy.” For most humans, channeling positivity is challenging, with good reason: “Because the human brain evolved during a time when danger was everywhere, it has a built-in negativity bias,” says Rick Hanson, Ph.D., a neuropsychologist and author of Buddha’s Brain: The Practical Neuroscience of Happiness, Love and Wisdom. “For humans to survive under these dire straits, the brain regions responsible for detecting threats had to be turbocharged. Evolution favored those who were able to react to danger with lightning speed.” Another way to explain it is that the brain is like Velcro for everything negative and Teflon for the positives. “An upsetting experience in our past can cast a long shadow,” Hanson confirms.

The Science Behind Negativity

The limbic system is partially responsible for these negative propensities. Located in the cerebral cortex and subcortex regions of your brain, it includes the hippocampus, which pulls together disparate information to help form memories, and the amygdala, a structure that is a key to recognizing danger. “The amygdala evaluates every situation, asking, ‘Is this good or bad?'” says Daniel Siegel, M.D., clinical professor of psychiatry at the UCLA School of Medicine and author of Mindsight: The New Science of Personal Transformation. Some scientists theorize that the amygdala may also be behind our ability to notice people’s fearful expressions faster than we do happy or neutral ones. In a study at Vanderbilt University, when scientists showed people pictures of faces on a computer screen through visual static (flashing images meant to camouflage the on-screen images), the subjects picked out the frightened faces more quickly than they did the calm ones. “A look of fear may signal a threat, so it makes sense that we’d be able to detect it quickly,” says David Zald, Ph.D., a researcher at Vanderbilt. In other words, pain takes precedence over pleasure, at least in the brain. Zald speculates that it may be the expression in someone’s eyes specifically—when someone is afraid, more of the white shows—that is key to our superswift fear-recognition skill.

The amygdala is also capable of registering “threat level red” before the conscious brain even catches on, Dr. Siegel says. I found this out years ago, one hot day when I was on a run. I stepped into the shade of an oak tree to cool off, but the instant my foot hit the ground, I jumped back, although I couldn’t explain why. Then awareness dawned, and I saw a rattlesnake coiled menacingly about 6 inches from where my foot had been.

The simple explanation for what happened in that fraction of a second is this: My occipital cortex, which processes visual cues, registered the snake and sent the image to my hippocampus and amygdala for a quick cross-check with things that fall under the “dangerous” category. That slithery shape was on the list, which triggered the release of powerful fight-or-flight hormones in my body—cortisol and adrenaline, to name a few. Thanks in part to that potent chemical cocktail, that near miss with a rattler has been etched into my memory ever since. Even now, 14 years later, glimpsing a slender, curvy stick on a trail is enough to make me stop dead in my tracks. The one-two punch of that brain mechanism and those stress hormones may explain why scary or upsetting memories often linger in vivid detail for years or even a lifetime, whereas happy recollections have a tendency to fade. The fearful memories are embedded in the brain so we learn from those situations and take pains to avoid them in the future.

How can the average human summon a lighter attitude in the face of all this seemingly preordained negativity? Falling in love with an effervescent pig is one way to do it. Another option: The same way you build up your biceps by doing curls, you can also shore up your capacity for hopefulness by consciously seeking out and concentrating on happy moments.

“There are a number of things you can do to strengthen the more highly evolved regions of the brain, such as the prefrontal cortex, along with the neural processes that are absolutely basic to our well-being and happiness, including the ability to be flexible, handle fear, feel empathy and be a person who acts in a moral way,” Dr. Siegel says.

One technique is simply to play a numbers game. The magic ratio of positive to negative emotions, research suggests, is to experience three joyful feelings for every bummer. “Three to one is the tipping point that leads to a happier life,” says Barbara Fredrickson, Ph.D., director of the Positive Emotions and Psychophysiology Lab at the University of North Carolina at Chapel Hill. By consciously increasing your positivity ratio, you can produce a net surplus of cheerfulness. Hanson adds, “By striving to seek out more upbeat encounters every day and savoring them to the max, you can gradually weave positive experiences into the fabric of your brain.”

That’s good news for your overall state of mind. People who are able to remain upbeat, even in the face of adversity, have high levels of activity in the left prefrontal part of the brain, according to brain scans done at the University of Wisconsin in Madison. These glass-halffull types also seem more adept at regulating the amygdala’s stress signals; they produce lower levels of cortisol when under pressure.

I’m getting a bit better at that every day. (Thank you, Chloe.) The last time I saw the potbellied pig, I realized I was smiling broadly, not simply because she’s such an endearing creature but because she was smiling at me. I could practically feel the cells in my left prefrontal cortex doing a happy dance.

And although there’s nothing like a grinning pig to bust a gal out of the blues, the exercise at right, along with the others on these pages, is also designed to bring on more smiles, even on gray Monday mornings. Test them out yourself and we promise you’ll look at the world differently, whatever the weather.

4 Easy Ways to Bring on the Calm

Smile. It can lift your mood, a phenomenon known as the facial feedback hypothesis. Similarly, researchers at the University of Wisconsin in Madison studied people before and after they’d gotten Botox, which blocks frowning. Post-‘tox, subjects took longer to understand sad or angry sentences. Impairing frowning may disrupt the brain-body feedback loop, dampening negative emotions.

Sing. There’s evidence that a primitive sensory organ in the inner ear, the sacculus, might react to music, triggering a response in the hypothalamus that creates a pleasurable buzz. “Consider singing your worries out loud in a lilting voice,” says Reid Wilson, Ph.D., author of Don’t Panic: Taking Control of Anxiety Attacks. (Try something like “Bills, bills, bills—they suck!” to the tune of “Row, Row, Row Your Boat.”) “Singing about worries makes them seem a bit absurd and helps put them in perspective.”

Sweat. “Exercise may buffer the brain from stressful situations,” says John Ratey, M.D., author of Spark: The Revolutionary New Science of Exercise and the Brain. There’s some evidence that working up a sweat promotes the growth of new neurons that are less reactive to stress.

Soothe. Replay a memory—cooking with your grandma—that evokes safety as you place your hand on your heart or cheek. “You’ll activate neural networks associated with feeling cared for, which can help you feel safer,” says neuropsychologist Rick Hanson, Ph.D. Another tip: Imagine yourself as a tree with a wide trunk and deep roots; visualize any upsetting things blowing around you like the wind. Hanson says, “They might rattle the leaves, but they can’t hurt the tree.” Or you.

Hang With Upbeat People

Emotions are contagious. “You can catch a mood, just like a cold,” says Marco Iacoboni, M.D., author of Mirroring People: The Science of Empathy and How We Connect With Others. When you watch a person doing something, the mirror neurons in your brain are activated, even if you’re not doing anything yourself. So if you see someone smile, your mirror neurons for smiling fire up, whether or not you’re in a good mood. “Spend time with happy people and you’ll eventually feel happier yourself,” Dr. Iacoboni says.

The trigger: Your sister hangs up on you. Before you have a conniption, close your eyes and breathe deeply. Feel any tightness in your body, then gradually start to let the tension go.

Think about any negative emotions you’re feeling. Fury? Shame? “Don’t judge yourself, whatever they are,” says James Baraz, coauthor of Awakening Joy: 10 Steps That Will Put You on the Road to Real Happiness. “The point is simply to become more aware of your emotions, which is key to controlling them.”

Now, name your ugly emotions. “I feel so humiliated.” When scientists at UCLA’s Brain Mapping Center showed people images of scared or angry faces, neural activity in the fear centers of their brain shot up. But when subjects described the facial expressions with one word, the activity dropped in the fear center and jumped in the prefrontal cortex. That suggests that labeling your feelings can calm the reactive amygdala. “But the words you use matter,” says author Daniel Siegel, M.D. “Instead of saying, ‘I am sad,’ which defines you, try ‘I’m feeling sad,’ which implies you recognize the emotion but aren’t consumed by it.” Make it a habit and you’ll create positive brain changes over time.

Get Blissed Out All Over

Hey. You with your face next to your phone. When’s the last time you stopped and looked at a sunset…or looked up, period? We thought so. But there’s good reason to stash the gadget and revel in what’s around you. Focus on pleasurable experiences and you’ll activate happiness-related neurons, which could make future good times feel more intense. “Simply put, when neurons fire together, they wire together,” says author Daniel Siegel, M.D.

How to do it. Experience joy with all your senses—inhale the smells; feel the air on your skin. “The more fully you feel something, the deeper the neural traces that are left behind in the brain,” says author Rick Hanson, Ph.D. “That solidifies your memory of the moment,” Over time, you’ll have an easier time handling random stressors. (Rude driver? No prob!)